1. Field of the Invention The present invention relates to heaters for seats, and more particularly to heater systems for aircraft seats.
2. Description of the Related Art
Between flights, aircraft frequently sit outdoors for prolonged periods of time, such as overnight. During such periods in winter, the temperature of the aircraft cabin decreases well below levels that are considered comfortable to passengers. Although the cabin usually is heated to room temperature before the passengers board, the seats often do not reach a comfortable temperature by boarding time. Seats on executive aircraft often are covered in leather, which is well known for being uncomfortable when cold. In addition, the application of heat to the lumbar region of the seat is useful for relieving back pain that may occur on long flights. Therefore, it is desirable to provide a heating mechanism in the aircraft passenger seats.
Unlike other types of vehicles, it is desirable that the interior of an aircraft be fabricated of materials that are flame resistant to provide time for the passengers to escape the aircraft cabin in the event of a fire upon landing. Electrical systems also must be very robust and have safeguards to avoid a fire hazard should a malfunction occur, because unlike an automobile, passengers may not be able to quickly exit an aircraft during a fire. It is further desired that electrical systems for passenger comfort related devices and amenities can be deactivated in an emergency so that such non-essential electrical loads do not adversely affect flight critical instruments and controls. Therefore, aircraft seat heaters have different design requirements than seats in other vehicles.
Incorporating seat heaters into aircraft seats presents additional challenges that do not exist with automobile seat heaters. For example, the seat bottom cushion of an aircraft seat may be removable for use as a floatation device after an emergency water landing. That removability can not be impeded by the seat heating system. Also, automobiles have a 12 volt direct current (VDC) electrical system, whereas aircraft typically have a 28 VDC system. In the event of a low resistance short circuit that does not draw high enough current to trip the circuit breaker, the greater voltage could result in sufficient power being delivered to ignite material adjacent the site of the short. Lightning frequently strikes aircraft and damage electronic devices Therefore many factors have to be considered when providing an aircraft seat heater system that do not have to be considered for automobile seat heaters.